Biologia, Bratislava, 61/Suppl. 20: S401—S411, 2006 Section Zoology DOI: 10.2478/s11756-007-0076-6
Holocene subfossil chironomid stratigraphy (Diptera: Chironomidae) in the sediment of Plešné Lake (the Bohemian Forest, Czech Republic): Palaeoenvironmental implications
Jolana Tátosová 1,JosefVeselý2 & Evžen Stuchlík3
1Institute for Environmental Studies, Faculty of Science, Charles University in Prague, Benátská 2,CZ-12801 Prague, Czech Republic; e-mail: [email protected] 2Czech Geological Survey, Geologická 6,CZ-15200 Prague 5, Czech Republic 3Hydrobiological Station, Institute for Environmental Studies, Charles University in Prague, P.O. Box 47,CZ-38801 Blatná, Czech Republic
Abstract: A faunal record of chironomid remains was analyzed in the upper 280 cm of a 543 cm long sediment core from Plešné jezero (Plešné Lake), the Bohemian Forest (Šumava, B¨ohmerwald), Czech Republic. The chronology of the sediment was established by means of 5 AMS-dated plant macroremains. The resolution of individual 3-cm sediment layers is ∼115 years and the analyzed upper 280 cm of the sediment core represent 10.4 cal. ka BP. As the results of DCA show, two marked changes were recorded in the otherwise relatively stable Holocene chironomid composition: (1) at the beginning of the Holocene (ca. 10.4–10.1 cal. ka BP) only oligotrophic and cold-adapted taxa (Diamesa sp.,M.insignilobus-type, H. grimshawi-type) were present in the chironomid assemblages, clearly reflecting a cool climate oscillation during the Preboreal period, and (2) during an event dated in the interval 1540–1771 AD, when most taxa vanished entirely and only Zavrelimyia sp. and Procladius sp. were alternately present accompanied by Tanytarsus sp. Although, the age of this event is in agreement with the dating of the Little Ice Age, the most probable reason for the elimination of many chironomid taxa was very low sums recorded in this part of the sediment, rather than cool conditions connected with the LIA. Variations in the chironomid fauna after the Preboreal period were reflected mainly by changes in abundances of dominant taxa rather than by changes in species composition. These variations could be explained by: (1) climatic changes, namely temperature and amount of rainfall resulting in oscillations in lake level, with changes in the occurrence of macrophytes in the littoral and (2) increasingly dense afforestation which led to a considerable input of organic material into the lake and a subsequent increase in the trophic status of the lake water. Key words: Chironomidae, glacial lake, climate changes, palaeoenvironmental reconstruction, palaeolimnology.
Introduction et al., 1997; Brooks & Birks, 2000). Chironomid lar- vae possess chitinized head capsules that are resistant Larvae of Chironomidae (Insecta: Diptera) colonize all to decomposition. Consequently, fossilized chironomid freshwater systems, from large lakes to the smallest head capsules tend to be well preserved in lake sed- ponds, and often dominate the benthos. This family iment over thousands of years, and can generally be is noted for its taxonomic richness, with nearly 10,000 identified to genus or, more rarely, to species-group species distributed globally (Cranston, 1995), repre- level. This offers the possibility of using the fossil chi- senting more than 20% of all freshwater insects in rivers ronomid record to infer past environmental conditions and lakes. As a result of their short generation times in lakes. Knowledge of modern chironomid ecology al- and the dispersal capacity of the winged adults, chi- lows the use of chironomid subfossils for the recon- ronomids respond rapidly to changes in a wide variety struction of palaeoproductivity (Brodersen & Linde- of environmental variables (Walker, 2001). Transfer gaard, 1999), acidification (Brodin & Gransberg, functions have been developed for a range of environ- 1993; Schnell & Willassen, 1996), palaeosalinity mental parameters including salinity (Heinrichs et al., (Walker et al., 1995) and, more recently, summer tem- 2001), dissolved oxygen (Quinlan & Smol, 2002) and perature variations (Brooks & Birks, 2001; Kor- nutrients (Brodersen & Lindegaard, 1999; Brooks hola et al., 2002; Heiri et al., 2003; Larocque & et al., 2001); however, over large climatic gradients, air Hall, 2004; Heiri & Lotter, 2005). temperature is often the best explanatory variable for The preliminary results presented here form part chironomid distribution (Lotter et al., 1997; Walker of a multi-disciplinary project investigating the biotic